The problem of deposit build-up in heat exchangers has been known for a long time and several solutions for this problem have been suggested.
In U.S. Pat. No. 2,978,378 a method for cleaning heat exchanger surfaces is described in which steel shot is scattered and allowed to drop against the inner surfaces of the heat exchanger so that deposits thereon are knocked off. The steel shot is recovered and recycled to the top of the heat exchanger.
U.S. Pat. No. 4,297,147 discloses a method for decoking fired heater tubes by stopping the normal operation of the heater and introducing a gas laden with steel shot into the inlet of the tubes at a certain velocity. A main disadvantage of this method resides in the requirement that the normal operation of the apparatus in question needs to be stopped. In U.S. Pat. No. 4,243,633 a reactor for the thermal cracking of a heavy oil is described which reactor is provided with a rotatable injection tube containing several nozzles which allow for the spraying of fluid against the inner wall of the reactor to remove deposits, such as coke.
From U.S. Pat. No. 3,888,302 a method for cleaning interior surfaces of a heat exchanger is known in which the normal operation of the heat exchanger can be continued during such cleaning. In this method a compound is added to the fluid to be cooled, which compound reacts with the deposits to render them volatile or friable. Evidently, such a method can only be used when deposits can react with such compounds and when the compound in question does not have any detrimental effect on any subsequent operation of the fluid, or, if the fluid is discharged, on the environment.
U.S. Pat. No. 4,461,651 describes a device for cleaning heat exchanger surfaces from deposits, which device employs sound energy vibration. The sound that is produced by the device procures vibrations to the particles in the deposits so that they fluidize. The device is to be constructed such that the distance between the surface to be cleaned and the device is between 10 and 15 feet.
It is an object of the present invention to provide a simple solution for the problem of cleaning inner surfaces of a heat exchanger while the normal operation of the heat exchanger may be continued and without the necessity to add alien compounds to the hot fluid.